Amazing entry! Feels like it was written for me. I love so much here: fitting a hexcrawl and a dungeon in this tight space, using venom as a key, the island sinking once the idol is stolen, clever magic items, weird shrines, sleepers from another age -- you've even got some Kim Holm art! The vocabulary you use is pitch-perfect for this theme: stygian, ebon, jet, ophidian, cyclopean... just an incredible entry here, really, really well done.
I did notice (what appears to me to be) an oddity on Room 5 of the temple, like maybe the green text block is occluding a line or two of the description block below. I don't think it hurts anything really, but it wouldn't be a jam without something to fix for the 1.1, eh?
Anyways, S-tier work! I expect we'll see this in the winner's circle, maybe even walking away with #1 theme.